US 6999728 B2
Method and device for the detection of one or more mobiles within a communications network, the method comprising at least one step for the “acquisition” of at least one RACH type signal exchanged between a mobile and a base station of the network and a step to measure the angle of arrival of the signal, the measurement step being synchronized with a parameter of the exchanged signal. Application to the GSM network.
1. A method for a detection of at least one mobile device within a communications network, said method comprising the steps of:
intercepting at least one signal exchanged between the at least one mobile device and a base station of the communications network;
acquiring a data of said at least one signal; and
measuring an angle of arrival of said at least one signal, wherein the step of measuring is synchronized with a parameter of the data.
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24. A device configured to detect at least one mobile device in a communications network, said device comprising:
a receiver configured to intercept at least one signal exchanged between at least one mobile station and a base station in the communications network;
a synchronizer configured to synchronize an activation of a measurement of at least one angle of arrival of said at least one signal in the device; and
a processor configured to process said at least one signal and configured to manage the synchronizer and the receiver.
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detecting an emergency call from the at least one mobile device by analyzing random access channel signals (RACH).
38. The method according to
estimating a road traffic by counting a number of mobile devices in an area.
1. Field of the Invention
The present invention relates to a method and a system for detecting and/or locating the presence of one or more mobile telephones (hereinafter called mobiles) in a communications network, by intercepting a signal exchanged between a mobile and the network. The network is for example a cellular communications network.
The invention can be applied especially in GSM networks.
It is used for example to detect and locate emergency calls.
It can also be applied to the measurement of road traffic density by the counting of the mobiles present in a given area, for example on a roadway.
It can also be applied in all cellular communications networks with known frequency and time-related characteristics, where the signals exchanged between a mobile and a base station have waveforms with a given structure and sequences of which there is a priori knowledge (for example learning sequences, synchronisation code etc).
2. Description of the Prior Art
The prior art describes various methods and devices suited to locating emergency calls and/or to measuring traffic density by means of the GSM network.
One approach, for example, lies in modifying the mobile radio stations or the SIM (Subscriber Identity Mobile) card in order to introduce a locating function within the radio mobile unit (which is generally of the GPS mini-receiver type or the type used for field measurements on server cells and neighboring cells) and a function of sending the results of measurements from the mobile, in the form of short messages, to the network, which uses them to locate the mobile. An approach of this kind however implies the adaptation or renewal of existing GSM radio mobile units. The number of these units corresponds at the present time to several hundred million all over the world.
Another approach consists in exploiting the network signaling function on the “Abis” interface or on the A interface. Using software that works at the network level, it is possible to locate radio mobile units by implementing various methods such as the measurement of radioelectrical fields, time difference of arrival (TDOA), tracking between cells etc. The interfaces <<Abis>> and <<A>> are described, for example, in X. Lagrange, P. Gdlewski and S. Tabbane, “Réseaux GSM-DCS” (GSM-DCS Networks) Editions Hermès Science, 4th edition.
However, these approaches have certain drawbacks:
An object of the present invention is a device and a method that can be used especially to detect mobiles present in a cellular type network or in a region covered by the network. The data are exploited in order to deduce, for example, road traffic density or again to locate emergency calls.
The invention relates to a method for the detection of one or more mobiles within a communications network. The method comprises at least one step for the “acquisition” of at least one signal exchanged between a mobile and a base station of the network and a step to measure the angle of arrival of the signal, the measurement step being synchronized with a parameter of the exchanged signal. The base station corresponds to the entry point of a mobile into a network.
The exchanged signal is, for example, sent from mobile to a base station of the network. The mobile may be called up at given points in time.
According to an alternative mode of implementation, the method comprises a step for dating the exchanged signal.
The step for measuring the angle of arrival is carried out for example for one or more values of angles in order to locate the mobile or mobiles.
The method may comprise a step to determine the propagation time of the signal between a mobile and a base station.
It may also comprise a step for the processing of the signal received by the base station, such as a demodulation step in order to determine the nature of the call and/or a step for sorting the signal on the basis of the information on the date and the demodulated data.
The method comprises for examples a step for counting one or more mobiles present in a given place in order to determine the corresponding density of mobiles.
The method can be applied to GSM communications networks and/or by using exchanged signals of the RACH type.
The invention also relates to a device for the detection of one or more mobiles in a communications network. The device comprises at least:
The element for the reception of the exchanged signals is, for example, an antenna network comprising five antennas.
The synchronization element and the signal reception element are integrated in one and the same element.
The processor is adapted, for example, to making goniometric measurements and managing the synchronization of the goniometry shots. It may also comprise a local application adapted to managing the information given by an interface of the Abis network.
The processor comprises for example a system application in order to centralize the data coming from the different local applications.
The invention also relates to a system for the detection of one or more mobiles within a communications network, comprising at least one device for the detection of one or more mobiles comprising one of the above-mentioned characteristics.
The direct exploitation of the radioelectrical signal sent and/or received by the radio mobile stations, independently of the cellular network that receives the system, the structure of the mobile stations and the radio electrical signals, gives the invention the following advantages in particular:
Other advantages and characteristics of the invention shall appear more clearly from the following description of exemplary embodiments of the device and of the method according to the invention given by way of an illustration, with reference to the appended figures, of which:
In order to provide for a clearer understanding of the present invention, the following description is given with reference to the detection of mobiles in a GSM network by way of an illustration that in no way restricts the scope of the invention.
Data transmission between the network and the mobiles (or the subscribers) uses for example BCCH/CCCH type multiframes (with common broadcast channels/control channels).
The frame exchanged between the base station and mobile comprises, for example, information necessary for synchronizing angle measurements or goniometric measurements according to a scheme that shall be explained further below in the description.
The invention consists especially of the use, within a cellular communications network, of a specific sensor for which an exemplary architecture is given in
The radioelectrical sensor 1 described in
The antenna is, for example, a calibrated network antenna. If necessary, it may be associated with filters at the head, centered on the GSM bands, more generally on the frequency bands of the network, in order to cancel the reception of co-site transmissions and thereby facilitate the installation of the system, for example on roadside pylons, in the vicinity of FM transmitters etc or again in any environment where the planned space is limited.
The switch 3 is a device known to those skilled in the art. It enables the calibration of the reception channels in amplitude and phase.
The six-channel receiver is for example a 300 kHz instantaneous band receiver provided with a calibration module for the phase and calibration of the sensor. Five channels are used for the goniometry for example (they receive the signals Si) and the sixth channel is used to synchronize the activation of the angle measurement or goniometry operation (this channel sends a synchronization signal Ssync).
The computer 6 is for example an industry-range PC type of microcomputer provided with two DSP boards specific to the driving of the receiver and the data-processing and signal-processing functions. It incorporates for example various acquisition and signal-processing boards which are equipped with software programs to run the measurement algorithms on the signals exchanged between the mobile or mobiles and the network. The software programs will be chosen for example as a function of the signal exchanged during the access to the network (known as RACH or random access channel signals) in the cellular networks.
The software with which the computer is equipped is adapted to detecting signals received by a mobile or a base station of the cellular network and to synchronizing the activation of the goniometric measurement by using, for example, a characteristic of the signal exchanged within a network.
According to one embodiment, it comprises:
The software program may also have a man-machine interface to insert planning and scheduling data pertaining to the network and transmit results obtained locally by the method according to the invention towards an appropriate processing center (not shown in the figures).
The computer has for example an input on the BTS (Base Transceiver Station). This is an apparatus consisting of radio transceivers and constituting the interface between the BSC (Base Station Controllers) and the mobiles (Abis probe).
In the case of an application pertaining to RACH signals, the sensor is adapted to implementing the following steps:
Without departing from the framework of the invention, it is possible to use several sensors organized in a system. These sensors can be used through means providing links to a data-processing center in order to produce measurements of traffic density (
According to another mode of implementation, the sensor according to the invention is associated with peripheral devices to facilitate the extraction of “network” data (in the preparation or initialization phase). The devices are for example logging or recording mobiles, GPS location systems, an extract from the network planning and scheduling data base given by the telecommunications operator, probe-type network devices for example on the Abis interface with the associated filters.
Examples of integration of the sensor into more complex structures are given in
Before explaining the implementation of such structures, the principle of the method implemented is explained here below in the case of a GSM network in which the RACH signals sent out by mobiles on standby are used.
Steps Implemented in the Method
The method according to the invention comprises, for example, the following steps:
1—A sensor, as described with reference to
2—calling up one or more mobiles on standby in order to prompt transmissions on their part (the generation of a transmission on the RACH channel for example). The transmissions are, for example, called for by means of a network procedure such as the <<location update>> procedure or the <<paging request>> procedure, or again naturally by using the planned settings (the case in which the excitation of the RACH channel is done outside a location update operation) for the management of the network. They may also be enforced by means of appropriate transmitters such as mobile base stations programmed for this purpose.
The mobile sends out a RACH signal, for example during a location area change or location zone change (ZLAC), a paging procedure, a location update procedure initiated by the mobile or an incoming/outgoing call or following a network loss (caused for example by scrambling or any other type of malfunction)
It is also possible to make use of periodic location update procedures with periods reduced to the hyperframe duration (about 6 minutes).
3—the computer 6 registers and processes the signals received in deferred time or processes the signals in real time at statistically significant time intervals given the period of the transmissions of the RACH signals. The time intervals depend, for example, on the mobile call-up method chosen in the step 2.
4—the computer 6 activates a step for the detection and counting of the access signals and mobiles on standby according to the methods known to those skilled in the art.
5—in a fifth step, the computer activates an angle measurement or goniometric measurement step. The measurement is activated for example by making use of
The five steps described in detail here above may be associated with the following steps:
6—the goniometry measurement step may be associated with a measurement of the propagation time of the mobile with respect to the BTS, (measurement of the Timing Advance): this makes it possible to associate a measurement of distance with the angle measurement and thus locate the mobile more efficiently.
7—by adding a step for the demodulation of the RACH signal intercepted on the radio channel (this is possible if the collaboration with the operator network is not sufficient) to the angle measurements or goniometric measurements, measurements of dating and mobile propagation time described here above, the computer may deduce the establishment cause (periodic location update, response to a paging operation, 112 emergency call expressed by the presence of a specific code in the message sent in the RACH signal); as well as
8—a recognition of the call making it possible to identify the establishment cause (periodic location, emergency call, etc.) and an identifier defining the caller (RA identifier of the RACH message for the GSM network) enabling a sorting of the calls.
The collaboration with the communications network makes it possible especially:
The location of the mobile is obtained, for example, by combining the measurements of the angle of arrival and the measurements of the traveling time or again by combining the measurements of the angle of arrival made on several sensors.
First Exemplary Application: Estimation of Road Traffic
In an exemplary implementation of the method according to the invention, the road traffic density is assessed by counting up the number of detections/locations of mobiles per elementary “road portion”. The basis of this function is the capacity to count transmissions associated with a location implementing the steps 1, 2 and 3 mentioned here above for the method.
When this application is associated with a demodulation of the RACH signals (above-mentioned step 7) either from the radio signal or by taking them at the Abis interface, it is possible to sort out the different calls such as location update, incoming/outgoing call etc.
Advantageously, the results of the road traffic density assessment can be improved by using the SDCCH and TCH signals on the corresponding frequencies, according to the lists of the frequencies allocated to the mobile.
These frequencies are either available after demodulation of the BCCH channels (analyzer terminal) or given by the network planning and scheduling system. To this end, an association of the different RACH signals sent out by a same mobile is necessary: this association is set up by exploiting these signals and the parameters, if any, demodulated in the radio signal and extracted from the signaling on the Abis interface (for example, known by the expressions <<establishment cause>> and <<random access>>).
The data produced take the form given in
According to another alternative implementation of the method, it is possible to separate mobiles present on the roads and also the traffic according to its direction without the identity of the mobile being known to the radioelectrical counting and locating system. To this end, several complementary options may be considered. Some of them are listed here below by way of an indication:
Use of Standardized Network Procedures Already Implanted in the GSM Cellular Communications Network
The operation of calling up the mobiles is prompted in certain cells of the network by a modification of the periodic “location update” procedures (indicated in the BCCH).
Probes on the Abis interfaces of the cells covered by the system (for example the cells managed by a same BSC) enable the calls to be sorted out and simplifies the work of the radio direction-finder by informing it of:
Other call-up operations are possible, implementing techniques specific to network management and to the logic of the itinerancy procedures:
The method according to the invention can also be used to detect an emergency call with the means used earlier to estimate the road traffic.
This method, along with the location of the mobile, necessitates accessing the contents of the message included in the RACH. These contents describe the establishment cause (namely the detection of the motive for the emergency call) either by demodulating the radio signal exchanged between the mobile and the base station or by using the network signaling (Abis probe).
The location of the emergency call is, for example, associated with an identification of the caller mobile, through the a priori knowledge of the identifier of the mobile (namely the TMSI). This identifier is either demodulated in the “paging response” or given by the signaling (Abis probe) enabling the network to retrieve the IMSI (International Mobile Subscriber Identity) by consulting the VLR (Visitor Location Register).
The bases of this emergency call location function are, for example:
The data given by the goniometric application are essentially:
The structure has a first daughter board 30 of the type with two fast acquisition channels which receives, firstly, the synchronization signal Ssync whose function is to synchronize the acquisitions of the signal Si exchanged between a mobile and the network, secondly a piece of information from a computer 32 equipped with a driver software program or master application software program. The software program is designed to drive the acquisition of the signal exchanged on the frequency concerned by the cell on which the emergency call is sought. The daughter board is directly connected to a second board or mother board whose function especially is to process the data.
This second board or mother board 31 is provided with a goniometric software program. It receives, firstly, the synchronization beep Tsync coming from the first daughter board and the signals Si received by the antenna network of the sensor (
The data given by this <<Abis>> application are essentially data on:
The structure interfaces for example between a base station controller (BSC) and the base stations (BTS). A data exchange is made for example between the Abis interface and the structure of the goniometric application to carry out the location method.